One of the parameters used to quantify the quality of particles such as carbon black is the surface area, as measured with respect to a gas such as nitrogen. Another parameter used to quantify the quality of the carbon black is the pore size distribution of the carbon black.
The surface area of a solid material has been determined in the past in an apparatus which operates in accordance with the Brunauer-Emmett-Teller (BET) equation given below: ##EQU1## where;
V is the volume adsorbed at equilibrium pressure P,
P.sub.o is the saturation pressure of the adsorbate at the adsorption temperature,
V.sub.m represents the monolayer capacity, and
C=exp [(E.sub.1 -E.sub.L)/RT] where E.sub.1 is the heat of adsorption of the first monolayer of adsorbate and E.sub.L is the heat of liquefaction of the adsorbate.
The pore size distribution can be calculated, inter alia, by either mercury porosimetry or the capillary condensation of nitrogen. Mercury porosimetry is usually limited to materials which have pore diameters in excess of 7.0 nanometers. Carbon blacks normally have a significant amount of porosity in pores which are less than 7.0 nanometers in diameter. To determine the pore size distribution of a carbon black, capillary condensation of nitrogen is a more suitable method and it can determine pore size distributions in the diameter range of from 2.0 to 30 nanometers using a method devised by Cranston and Inkley. The Cranston and Inkley method for estimating the pore size distribution of a material requires the determination of a isotherm or several isotherms at different temperatures. For example, a suitable isotherm should be the ratio of the saturation pressure of nitrogen at one atmosphere pressure and 77.degree. K. (P.sub.o) to the equilibrium adsorption pressure of nitrogen in torr (P.sub.i) less than P.sub.o. The variables are moles of gas and pressure. The P.sub.i /P.sub.o ratio should be measured for values from zero to one. With a determination of the isotherm, the pore size distribution can be estimated by the formula of Cranston and Inkley given below: ##EQU2## where v.sub.r .delta.r is the total volume of nitrogen adsorbed (as liquid) and V.sub.r .delta.r is the total volume of pores in the range .delta.r considered.
Heretofore, an apparatus which could measure the pore size distribution or the surface area of a carbon black with respect to a given gas such as nitrogen as either extremely cumbersome or limited in the number of determinations that could be made at a given time. Thus, a compact apparatus for screening multiple samples of solid particles such as carbon black would be highly desirable.